Transmission and constant speed accessory drive

ABSTRACT

A method of operating a belt drive accessory system comprising the steps of transmitting a torque with a first endless member from a driver member to a planetary ball transmission input, coaxially aligning the planetary ball transmission input with a planetary ball transmission output, transmitting a torque by a second endless member from the planetary ball transmission output to a driven accessory, selecting a speed ratio of the planetary ball transmission according to a driver member rotational speed, thereby operating the driven accessory at a substantially constant speed at a point of substantially maximum efficiency over a drive member rotational speed range, and frictionally locking the speed ratio of the planetary ball transmission when a drive member speed is constant.

REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims priority from U.S.nonprovisional application Ser. No. 10/780,979 filed Feb. 18, 2004.

FIELD OF THE INVENTION

The invention relates to a transmission and to a constant speedaccessory drive utilizing same, and more particularly, to a infinitelyvariable speed ratio planetary ball transmission having a plurality ofplanetary members in rolling contact with an inner and outer race and abelt driven constant speed accessory drive for operating engineaccessories at a substantially constant speed.

BACKGROUND OF THE INVENTION

Vehicle engines generally comprise certain accessories that are used inthe operation of the engine and vehicle. Such accessories can include apower steering pump, an air conditioning compressor, an alternator, anoil pump, a fuel pump and so on. These accessories are generally drivenby a serpentine belt. The serpentine belt engages a pulley on eachaccessory as well as on an engine crankshaft. The engine crankshaftprovides the torque to drive the accessories.

As the belt is driven by the crankshaft it is necessarily subject toengine speed variations during acceleration and deceleration of thevehicle. In other words the operating speed of the accessories isdirectly proportional to the speed of the engine. The variations inengine speed result in inefficient operation of the accessories becauseeach accessory must be designed to operate satisfactorily over theentire engine speed range. This necessarily means that the efficiency isless than optimum for most of the speed range. Therefore it is desirableto decouple the accessories from the crankshaft so they can be driven ata constant, optimum speed.

Representative of the art is U.S. Pat. No. 4,969,857 to Kumm (1990)which discloses a variable speed accessory drive having a flat beltdriving a variable diameter pulley wherein a fixed diameter pulleyattached to the variable diameter pulley is used to drive another beltcoupled to the accessories.

Also representative of the art is U.S. Pat. No. 4,305,488 to McIntosh(1981) which discloses a vehicle accessory drive assembly thatincorporates a speed-increasing planetary gear set with an engine drivencarrier input.

Kumm represents a particularly complex response to the problem,requiring many component parts in the CVT pulley which must operate inconcert to perform properly. Further, Kumm will not operate with amultiple-ribbed belt which is the predominant driver in accessorydrives.

A simple planetary ball continuously variable transmission is desirableto reduce possible failure modes for an accessory drive system as wellas to increase durability.

Representative of the art is U.S. Pat. No. 6,461,268 B1 to Milner (2002)which discloses a continuously variable transmission of the type havingplanetary members in rolling contact with radially inner and outer raceseach comprising two axially spaced parts with control means forselectively varying the axial separation of the two parts of one race.

What is needed is a method of operating a belt drive accessory system byfrictionally locking the speed ratio of a planetary ball transmissionwhen a drive member speed is constant. The present invention meets thisneed.

SUMMARY OF THE INVENTION

The primary aspect of the invention is to provide a method of operatinga belt drive accessory system by frictionally locking the speed ratio ofa planetary ball transmission when a drive member speed is constant.

Other aspects of the invention will be pointed out or made obvious bythe following description of the invention and the accompanyingdrawings.

The invention comprises a method of operating a belt drive accessorysystem comprising the steps of transmitting a torque with a firstendless member from a driver member to a planetary ball transmissioninput, coaxially aligning the planetary ball transmission input with aplanetary ball transmission output, transmitting a torque by a secondendless member from the planetary ball transmission output to a drivenaccessory, selecting a speed ratio of the planetary ball transmissionaccording to a driver member rotational speed, thereby operating thedriven accessory at a substantially constant speed at a point ofsubstantially maximum efficiency over a drive member rotational speedrange, and frictionally locking the speed ratio of the planetary balltransmission when a drive member speed is constant.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe specification, illustrate preferred embodiments of the presentinvention, and together with a description, serve to explain theprinciples of the invention.

FIG. 1 is a schematic of a constant speed accessory drive system.

FIG. 2 is a cross-sectional view of the transmission.

FIG. 3 is a partial cross section of the races showing a maximum driveratio.

FIG. 4 is a partial cross section of the races showing a minimum driveratio.

FIG. 5 is a partial cross section of the races.

FIG. 6 is a partial cross section of the cage.

FIG. 7 is a cross section of a follower assembly.

FIG. 8 is a detail of the housing and outer race.

FIG. 9 is a detail of the outer race drive.

FIG. 10 is a cross-sectional view of the transmission.

FIG. 11 is a perspective view of the tandem embodiment.

FIG. 12 is a partial perspective view of the tandem embodiment.

FIG. 13 is a block diagram of the control system.

FIG. 14 is a graph showing improved vehicle performance.

FIG. 15 is a graph showing accessory speeds compared to a crankshaftspeed.

FIG. 16 is a graph showing accessory speed compared to crankshaft speedsfor a proportionally driven prior art system.

FIG. 17 is a graph showing speed ratios for the transmission.

FIG. 18 is a graph showing an exemplary European drive cycle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The inventive system comprises a constant speed accessory drive (CSAD)that significantly reduces parasitic energy losses of drivenaccessories. The system results in significantly improved vehicleperformance and drivability, including vehicle drive output torque andfuel economy improvements.

The system comprises an infinitely variable ratio planetary membertransmission used in a belt driven engine accessory system that allowsengine accessories to be operated at a substantially constant speed asthe engine, and hence crankshaft, speed continuously varies. Bymaintaining the accessory belt drive at a minimum speed that meets allof the requirements of the vehicle, i.e., the minimum speed at whichalternator delivers needed current and at which the air conditionerdelivers required cooling, the system significantly reduces theaccessory torque loads imposed on the engine. This makes more outputtorque available for vehicle propulsion, or, reduces the amount ofthrottle (power) needed to maintain the vehicle at a constant speed. Anoptimum situation is realized when the minimum accessory driven speed isless than the crankshaft speed, taking into account differences in thediameters of the respective accessory pulleys. In order to illustratethe advantages of the inventive CSAD system, vehicle acceleration andfuel consumption are described as indicative elements of performance.

A general arrangement of the constant speed accessory drive system isshown in FIG. 1. Driver pulley (A) is connected to a prime mover such asthe crankshaft of a vehicle internal combustion (IC) engine. The ICengine example is not offered as a limitation since the inventive systemmay be used in most any situation where it is desirable to control orvary a driven member speed with respect to a driver speed.

Driven pulley (B) is the input pulley 100 of an infinitely variabletransmission 1000 of the type described herein. A first endless belt B1is engaged between pulleys (A) and (B) thereby directly coupling thedriver pulley to the driven pulley in a two point drive configuration.The speed of driven pulley (B) varies directly as the speed of thedriver pulley (A) varies. Belt B1 may comprise any belt profile known inthe art, including multiple-ribbed, v-belt and toothed.

Transmission 1000 drives various accessory pulleys by way of outputpulley 101 that is connected by a second endless belt (B2) to drivenaccessories, including but not limited to an alternator (ALT), waterpump (WP), and power steering pump (PS). Another accessory, namely anair conditioner (AC) compressor is shown directly connected totransmission 1000 and thereby to the output shaft of the transmission asdescribed elsewhere in this specification. In an alternative arrangementthe AC compressor need not be connected directly to the transmission andcan be located elsewhere on the engine engaged with belt B2 as are theother accessories.

The disclosed drive arrangement decouples the crankshaft from the drivenaccessories, allowing the rotational speed of the accessories to bevaried by the transmission independently of the crankshaft speed.Decoupling the accessories in this manner serves to increase theefficiency of the accessories and of the engine.

A belt tensioner T is used to tension belt B2 in order to facilitatetorque transfer from the transmission output to the accessories.Tensioner T may also comprise damping, including asymmetric damping asknown in the art.

The transmission mechanism described herein is extremely compact andhighly efficient. The design eliminates any need for a pressurizedhydraulic circuit for either lubrication or control of the transmission.

Description of the Infinitely Variable Ratio Transmission

In FIG. 2, a cross-sectional view of the transmission and itsadvantageous dual output features are shown. Transmission 1000 comprisesa device of the type known generally as a continuously variabletransmission (CVT). The transmission comprises planetary members inrolling contact with radially inner and outer races. Each race comprisestwo axially spaced parts or portions. Control means responsive to anengine speed are used to selectively vary an axial separation of the twoparts of the outer race and thereby a radial position of the planetaryball members in rolling contact with the races. The variation in theradial position of the planetary members varies the output ratio andhence a rotational speed of the transmission output shaft.

Means sensitive to the torque applied to an input member of thetransmission operates to determine a compensating variation in theseparation of the two parts of the inner race and thus the ratio of thetransmission. The torque sensitive means also varies the forcesexchanged between the planetary members and the races, normal to theinterface between them (N). The transmission is more fully described inU.S. Pat. No. 6,461,268 to Milner, the entirety of which disclosure isincorporated herein by reference.

The transmission depicted in FIG. 2, sometimes also referred to as avariator or infinitely variable transmission, comprises housing 5 withinwhich is rotationally mounted a planet cage 14. Planet cage 14 comprisesportions 14 a and 14 b. An input drive member comprising input shaft 11is mounted coaxially within planet cage 14 on bearing 12 and bearing 13.Bearing 13 may comprise any suitable bearing known in the art, includingbut not limited to ball bearings and needle bearings. Snap ring 86retains bearing 13 in planet cage portion 14 b. Press fit ring 12 aretains bearing 12 in plant cage portion 14 a. Planet cage 14 isrotatably mounted within housing 5 on bearings 46, 47. Bearings (46,47)may comprise any suitable known in the art such as ball bearings orneedle bearings. Snap ring 85 retains bearing 46 on planet cage portion14 b.

Planet cage portions 14 a, 14 b are joined together by shafts 16. Shafts16 comprise studs, one end of which is press fit into portion 14 a. Theother end is cooperatively engaged with portion 14 b and may comprise apress fit as well.

Seals (76, 78) contain the traction fluid within the transmission andprevent intrusion of foreign material into the transmission.

An axial cylindrical extension 22 of portion 14 a constitutes one of twocoaxial output drive members or shafts of the transmission. The otheroutput shaft 102 is an axial extension of portion 14 b. One can see thatoutput shafts 22 and 102 rotate at the same speed since each ismechanically connected to planet cage 14.

Planet cage 14 is the means by which torque is transmitted from theinput shaft 11 to the output shafts and pulley 101. To accomplish this,planet cage 14 further comprises four planet follower members 15disposed symmetrically about the axis of input shaft 11 between theinner races (23 a, 23 b) and outer races (26 a, 26 b). Each planetaryfollower member 15 is rotatably borne by planet cage 14 on planetfollower shafts 16. Each member 15 is rotatably borne upon each shaft 16by needle bearings 60, or any other suitable bearing known in the art.Each follower 15 may move axially along each shaft 16 in response to amovement of each planetary member 25, see FIG. 3.

Follower members 15 comprise a concave arcuate profile approximated bytwo truncated cone forms coaxially joined on a major axis of each, seeFIG. 7. The conical form of each follower member provides anadvantageous means of engaging a follower member with a sphericalplanetary member 25. Namely, the arcuate concave form provides twopoints of contact between the follower 15 surface and a planetary member25 surface, thereby substantially decreasing engagement forces andthereby increasing durability under high loads as compared to a singlepoint of engagement.

Turning now to the rotating assemblies, input shaft 11 comprisesradially inner race which comprises two inner race parts 23 a and 23 b.Part 23 a is formed as an integral part of shaft 11 or may also comprisea separate part that is press fit onto shaft 11. Parts 23 a and 23 beach comprise arcuate surfaces 27 a and 27 b respectively upon whichplanetary members 25 roll.

Part 23 b is an adjustable member and is axially moveable along shaft 11by a helical interengagement means comprising a ball screw threadedengagement, see FIG. 3. The ball screw comprises cooperating threadflights or helical channels 37 and 38 with rolling elements or balls 39cooperatively disposed therein, see FIG. 10. Helical channels 37 and 38and balls 39 can alternatively be replaced by a known threadedengagement, for example “ajax” or “acme” threads on part 23 b and inputshaft 11.

By virtue of the helical form of the channels 37, 38 a relative rotationof the input shaft 11 and part 23 b in one directional sense will causepart 23 b to be axially displaced towards part 23 a. Axial separation ofthe two parts 23 a, 23 b of the inner raceway occurs where there isrelative rotation between part 23 b and input shaft 11 in the oppositedirectional sense.

Part 23 b is held in continuous light contact with planetary members 25by helical interengagement means biasing member 40. Biasing member 40comprises a torsional spring and has an end engaged with a limit onshaft 11 at member 41 and the other end engaged with part 23 b. Spring40 is under continuous compression so that part 23 b is continuouslyurged axially along and upon shaft 11, resulting in a relative turningmotion causing a relative axial displacement of part 23 b, therebycausing continuous engagement of part 23 b with planetary members 25.

Outer race 26 comprises axially separable annular race parts 26 a, 26 b.Outer race 26 comprises part 26 a which has an axially extendingcylindrical portion 42 within which the second of the radially outerrace part 26 b is rotatably engaged. Part 26 a and part 26 b arerotationally connected by a helical interengagement means, thecombination comprising means for selectively varying the axialseparation of the race parts. Namely, an inner surface of thecylindrical portion 42 has a helical channel 43. Radially outer racepart 26 b is an adjustment member and has on its outer cylindricalsurface a helical channel 44. Rolling elements or balls 48 having arolling engagement are disposed between channel 43 and channel 44allowing outer race part 26 b to rotate with respect to portion 42.Channel 43, channel 44 and balls 48 together form a ball screw. Channels43, 44 have a pitch coarse enough to effect timely ratio changingbetween extremes without requiring excessive travel of the ratio changeworm gear, see FIG. 9, while not being so coarse that the contactconditions simply force the races apart. Channels 43, 44 and balls 48may also be replaced with a threaded engagement, including “ajax” or“acme” threads. An angular movement or rotation of outer race part 26 bwith respect to part 26 a to effect a full ratio change is approximately150°.

Planetary members 25 roll along the rolling tracks of the race members.Rolling tracks of the inner race parts 23 a, 23 b and outer race parts26 a, 26 b, respectively identified 27 a, 27 b and 28 a, 28 b eachcomprise, in cross-section, a partially-circular arcuate surface theradius of which is slightly greater than the radius (RS) of eachspherical planetary member 25.

The difference in radius between each planetary member 25 and tracks 27a, 27 b, 28 a, 28 b causes a theoretical point engagement between eachmember 25 and each track. A radius of curvature of surface 27 a and 27 bcan be selected to give a desired rate of ratio change based upon a rateat which the members 25 move radially during such ratio change.

The contact patches between members 25 and surfaces 27 a, 27 b, 28 a, 28b should not be too large in order to avoid so-called spin lossresulting from forces developing in the hydrodynamic fluid between thetwo elements in rolling contact. Disposed between parts 23 a and 23 b isgallery 70 which provides a return flow path for traction fluidcirculating among members 25 and the inner and outer races.

Through operation of the actuator and worm drive, axial approach of thetwo outer race parts 26 a, 26 b controls the radial position of theplanetary members by applying pressure to the planetary members 25thereby causing them to move radially inwardly toward input shaft 11thereby urging the two inner race parts 23 a, 23 b apart. This changesthe output ratio of the transmission. Torsion spring 40 assurescontinuous engagement of race part 23 b with members 25. Of course,outer race parts 26 a and 26 b may also move apart, thereby causing theplanetary members to move radially away from input shaft 11, therebyallowing parts 23 a and 23 b to move axially toward each other throughoperation of the torque sensitive means.

Race part 26 a rotates within indentations in housing 5 while moving inan axial direction which is parallel to axis X-X for ratio changes. AxisX-X is the common axis of rotation of the transmission, including theinput shaft 11, the inner and outer raceways 23, 26, the output shafts22, 102, as well as being the center of the orbital path of thespherical planetary members 25. Race part 26 b engages housing 5 in sucha manner so as to prevent rotation of part 26 b with respect to housing5, but in a manner to otherwise allow axial movement of part 26 b towardor away from part 26 a as part 26 a rotates.

The transmission also possesses an inherent one-way clutching actionbased on the operation of the torque sensitive mechanism. During highdeceleration rates where the component inertia torques are enough toovercome the friction and load torques, the normal output will becomethe driver in the transmission. This causes the clamping force on theinner race 23 b to be reduced and an overrunning condition will exist.

Housing 5 comprises a somewhat rectangular form in cross section. Studs71 connect housing side 72 and housing side 73 with housing 5 using nuts74, see FIG. 8. Cooling fins (CF) extending from the outer surface ofthe housing 5 may be used to cool the transmission and traction fluid.

Housing 5 comprises reservoir 75 which receives and contains thetraction fluid for the transmission. The traction fluid system isunpressurized and instead operates at an ambient pressure condition.Cage 14 rotates partially submerged in the traction fluid contained inreservoir 75. The traction fluid is swept up into the rotating portionsof the transmission during operation. The traction fluid provides therequired coefficient of friction between the planetary members or ballsand the race surfaces. The fluid flows around the planetary members andexits the outer race through gap 77 and inner race through gap 70. Thetraction fluid also cools the transmission.

The traction fluid can comprises any of those suitable for the serviceknown in the art, which includes Santotrac® 50 or Santotrac® 2500. Eachfluid is a low viscosity synthetic hydrocarbon based traction fluid usedwhere medium to high film strength is desirable. The fluids areavailable from Findett Corporation, 8 Governor Drive, St. Charles, Mo.63301.

Housing 5 further comprises means for mounting to an engine, see FIG.11.

Although this description includes an automotive oriented constant speedaccessory drive system, it should be understood that the inventivetransmission can be used in any application requiring a transmissiondisposed between a driver and driven equipment. In these cases thedriver may be directly coupled to the input shaft 11 of the transmissionas well as by belt and pulley. The inventive transmission can be used,for example and not by way of limitation, in vehicle or motorcycledriveline applications such as transmissions, as well as slurry pumps,water pumps, air and gas compressors, HVAC, air handling equipment, bulkmaterial handling pumps, and so on. In each case the equipment is drivenby a primary driver such as an electric motor or internal combustionengine. The transmission is disposed between the motor or engine and thedriven equipment or driveline. The continuously variable feature of thetransmission allows infinite and accurate speed control of the drivenequipment speed. The inventive transmission provides the advantage ofoffering the widest possible range of speed ratios for a drive systemrequirement as compared to a gear type transmission. Further, the dualoutput feature of the transmission allows two pieces of equipment to bedriven by a singe transmission while utilizing a single driver. If abelt drive with a transmission output, then multiple pieces of drivenequipment can be driven at different speeds.

Description of Operation.

In operation, input drive shaft 11 is driven by belt B1 engaged withpulley 100. Rotation of the input drive shaft 11 causes inner race 23 torotate and carry with it on surfaces 27 a and 27 b, by rolling contact,the planetary members 25 which roll upon the curved surfaces 28 a and 28b of outer race 26. Planetary members 25 are constrained by theircontact with the curved surfaces 27 a, 27 b and 28 a, 28 b of theradially inner and radially outer races 23, 26 respectively. Since innerrace part 23 a is fixed in position with respect to shaft 11, all radialand axial movements of the spherical members 25 is defined by and inreference to part 23 a. Hence the path followed by a center of eachmember 25 describes a curve that matches the arcuate shape of surface 27a.

The mechanism operates as a torque-sensitive means which allowscompensating rotary and axial movement of the movable inner race part 23b with respect to fixed race part 23 a. The torque sensitive meanscomprises biasing member 40 and helical interengagement means 37, 38,39, acting to react the forces exerted by the transmission of driveforces between the radially inner race 23 and the planetary members 15.The torque sensitive means acts both to determine the compensatingvariation in the separation of the parts of the inner race 23 and thusthe transmission ratio of the device, and to vary the forces exchangedbetween the planetary members 15 and the races normal to the interfacebetween them.

Put another way, the torque sensitive helical interengagement meansreacts a direct circumferential force and an axial force having acircumferential component. The circumferential component of the axialforce is substantially equal to and opposite in sign from the directcircumferential force reacted by the helical interengagement. Thisminimizes the force required to be applied to the control means forselectively varying the axial separation of the two axially spaced partsof the outer race to maintain or change a transmission ratio of thetransmission.

Each planetary member 25 is also rotationally engaged with a followermember 15. Planetary motion of the members 25 is conveyed to thefollower members 15 and, via the shafts 16, to the planet cage 14 whichis in turn connected to output shafts 22 and 102. Since members 25 moveboth radially and axially with respect to shaft 11 during ratio changesof the transmission each follower member 15 is also slightly moveableaxially on bearings 60 in a direction parallel to axis X-X so thatproper contact with each member 25 is maintained through the entirerange of motion of each.

Ratio change of the transmission is effected by variation in therelative approach or separation of the radially outer race parts 26 a,26 b. This is caused by rotation in one direction or the other of outerrace part 26 a by worm drive 90. Rotation of outer race part 26 a causesa greater or lesser force to be applied to the planetary members 25urging them radially inwardly toward inner race 23. As the two outerrace parts 26 a, 26 b are brought together the forces exerted on theplanetary members 25 increases. The radially inward force applied toinner races 23 a, 23 b urges them apart caused by relative rotation ofrace part 23 b with respect to shaft 11 through operation of the balls39 in the channels 37, 38.

Race part 23 b rotates at the same speed as race part 23 a apart from aminor transient variation when relative movement over a limited arctakes place for compensating adjustment of the pressures applied by theplanetary members 25. More particularly, rotation of shaft 11 in theintended direction of drive causes the race part 23 b to approach part23 a axially when resisted by drag so that any play in the rollingcontact between the races and the planetary members 25 is taken up untilthe forces exerted on the helical interengagement by race part 23 b andthe drive shaft 11 matches the reaction forces between the race part 23b and the planetary members 25. At this point no further axialdisplacement of the race part 23 b relative to race part 23 a takesplace.

A transmission ratio is determined by the radial position of the racepart 26 a and in turn, of planetary members 25. The function of theinner race threads 37, 38 and balls 39 is to maintain the ratio ofnormal to tangential (tractive) force (n/f) of each planetary member 25contact point within a certain range. The ratio must be large enough toensure that excessive slip does not occur (at least n/f=10 for partiallubrication and up to twice that for full hydrodynamic lubrication) butnot so large that a significantly greater normal force (N) is appliedthan is needed, which would reduce efficiency, torque capacity and lifeof the unit.

A spherical planetary member 25 shape is well suited for this rolebecause such a planetary member is in equilibrium under the action offour peripheral contact radial ‘squeezing’ forces applied by the racesin the plane of FIG. 2 (the y direction) and a driving force through themember center normal to the plane of the drawing (the z direction), ashere, y/z has the same value wherever on the periphery the contactpoints may be. This means that the inner and outer race y/z values areequal for any ratio setting of the transmission. Torsion spring 40acting on an inner race 23 b provides sufficient preload to ensure thatthere is always enough contact pressure for the torque sensitivemechanism to function as the torque increases from zero.

Housing 5, with end portions 72 and 73, contains the variabletransmission unit in its entirety with the exception of the input andoutput shafts and worm drive, rendering the overall package verycompact. Hence, the invention is very suitable, for example, for thetransmission for a constant speed accessory drive. For use in anaccessory belt drive system an output from transmission 1000 comprises amultiple-ribbed pulley on output shaft 22. Another output shaft 102extends coaxially opposite shaft 22. Shaft 102 can also be directlycoupled to an accessory, such as an air conditioner compressor, see FIG.11. The combination of the transmission, mounting bracket and attachedaccessory comprise a complete assembly that is mountable as a singleunit on a vehicle engine. Of course, the air conditioner compressor(A/C) is only offered as an example and any other accessory may bemounted to the transmission as well, including without limitation apower steering pump, alternator, fuel pump, oil pump, water pump, aswell as any other accessory.

It should be noted that the input and output members may have theirrespective functions reversed, that is, the input may be receivedthrough shaft 22 and the output transmitted out through shaft 11. Thisresults in an increase in the output torque over the input torque.Hence, the transmission may be operated in either rotational torquetransmitting direction.

In the race configuration illustrated in FIG. 3 the radius of rollingcontact (R1) between the members 25 and the inner raceway 23 isrelatively large and the radius of contact (R3) between the members 25and the outer raceway 26 is relatively small. In this configuration thetransmission ratio between the input shaft 11 and output shaft 22, 102is approximately 1.0. As described elsewhere in this specification, theradius of rolling contact is controlled by the relative position ofparts 26 a and 26 b. The axial position of part 26 b is controlled byworm drive 90, see FIG. 9. Action of worm drive 90 on part 26 a axiallymoves part 26 b by partially rotating part 26 a about shaft 11 in eithera clockwise or counterclockwise direction.

Referring to FIG. 4, by operation of worm drive 90 in an oppositedirection from that illustrated in FIG. 3, race part 26 b moves axiallytoward part 26 a as part 26 a rotates so that the members 25 are forcedto move radially inwardly. Movement of members 25 is compensated byaxial approach of the inner race part 23 b toward part 23 a as caused byaction of torsion spring 40 bearing on part 23 b. In this configurationthe radius of rolling contact (R2) between the members 25 and the innerrace 23 is relatively small and the radius of contact (R4) between themembers 25 and the outer race 26 is relatively large. In thisconfiguration, the transmission ratio between the input shaft 11 andoutput shaft 22, 102 is approximately 0.3.

Since inner race part 23 a does not move, the members 25 roll on surface27 a and thereby follow the contour of surface 27 a. The center of eachmember 25 moves approximately in direction D2, displacing radiallyinwardly and axially simultaneously as the ratio is changed from FIG. 3to FIG. 4.

The input/output ratio is also subject to the relative diameters of theinput 100 and output 101 pulley, thereby adding another dimension ofvariability to the inventive system. For example, the diameter of outputpulley 101 may be matched to cooperate with the diameter of each of theaccessory pulleys. Properly selecting the diameter of each pulley in thesystem allows the desired rotational speed to be realized for eachaccessory for a corresponding engine crankshaft speed. The differingpulley ratios are enhanced by the infinitely variable characteristic ofthe transmission.

FIG. 5 is a cross sectional perspective view of the shaft and races.Inner race 23 and outer race 26 are shown. Inner race part 23 b moves indirections ±D by rotating about input shaft 11 on the ball screw (37,38, 39). Outer race part 26 b moves in directions ±D as well by virtueof rotation of outer race part 26 a in direction R on ball screw 43, 44,48, see FIG. 10. Fluid gallery 77 provides a path for circulatingtraction fluid to leave the cage and race area and return to reservoir75. The axis of rotation of the transmission is noted by X-X.

FIG. 6 is a partial cross sectional view of the cage. Cage 14 comprisescage portion 14 a and cage portion 14 b. Follower brackets 80 aredisposed symmetrically about cage 14. Each shaft 16 is connected to abracket 80, and thereby cage 14, in holes 82. Dowel pins 84 disposed inholes 81 are used to properly align cage portions 14 a and 14 b. Aplanetary member 25 rolls within a respective space 83. Spaces 83 aresymmetrically disposed about cage 14 between follower brackets 80. Snapring 86 engages portion 14 b in groove 96. Output shafts 22 and 102extend from cage portion 14 a and 14 b respectively.

FIG. 7 is a cross sectional view of the follower assembly. Follower 15comprises an arcuate form having a cross section which is approximatedby two truncated cones joined point to point. This results in asubstantially concave cross section having radii A1 and A2 which engagemembers 25. Radius A1 can be equal to or greater than radius A2. Thisform is advantageous because it affords two points of contact with eachball 25 and follower 15. This provides improved efficiency and accuracyfor torque transfer. It also reduces the loading from a single point totwo points without significantly increasing rolling friction losses. Inorder to follow each member 25 as a ratio is changed, follower 15 isslightly moveable axially in direction M on needle bearings 60 alongshaft 16. Needle bearings 60 are contained between shoulders 61, 62 onshaft 16. Shoulders 61, 62 for containing bearing 60 may comprise snaprings known in the art as well. Follower 15 is shown axially displacedon shaft 16.

FIG. 8 is a detail of the housing and outer race. Housing comprisessections 72, 73. Outer race part 26 b is shown with dowels 26 c. Dowels26 c engage holes in housing section 72. Race part 26 b is freelymoveable in an axial direction (with respect to axis X-X) upon dowels 26c as outer race part 26 a is rotated by worm drive 90. Dowels 26 cconstrain outer race part 26 b from rotating as part 26 a rotates.

Studs 71 and nuts 74 hold housing sections 72 and 73 together. Coolingfins CF are mounted to an outer surface of housing 5 and radiate heatfrom the transmission.

FIG. 9 is a detail of the race drive. Worm drive 90 is attached tohousing 5 using known means for example studs, bolts or screws. Wormdrive 90 comprises a DC stepper motor 96. By way of example and not oflimitation a suitable stepper motor is manufactured by LIN Engineering,model number 4218L-01. The step motor can be viewed atwww.linengineering.com/our products/4218.htm. Other stepper motors knownin the art may be used as well. Stepper motor controller 97 is known inthe art as well and may be obtained from LIN Engineering or othersuitable supplier.

Sprocket 91 is connected to the output shaft of the motor 96. By way ofexample, sprocket 91 comprises 30 teeth and a pitch diameter of 28.65mm. A cooperating sprocket 92 is attached to the worm drive pinion 94.By way of example, sprocket 92 has 15 teeth and a pitch diameter of14.32 mm. Hence, the drive ratio in this non-limiting example is 2:1.Toothed belt B3 is entrained between sprocket 91 and 92 and comprises 45teeth and a 3 mm pitch, for a total pitch length of 135 mm.

Worm gear 93 is machined into the drive pinion 94. A cooperating wormgear track 95 is machined into the outer race part 26 a. An exemplaryworm gear set is available from W.M. Berg at www.wmberg.com, stocknumber WCS-7S. For example, worm 93 comprises a single thread with apitch diameter of 12.0 mm, a lead of 3.14159 mm, a lead angle of 4.75degrees, and a pressure angle of 14.5 degrees. The pitch diameter ofworm gear 95 is 88 mm and comprises 88 teeth. Thus, the module is 1.0.The helical angle is 4.75 degrees, the pressure angle is 14.5 degreesand the circular pitch is 3.14159 mm. The center distance of the wormgear set will be 50.00 mm (½ of (88+12)) and the ratio is 88:1.

A frictional component is created between the pinion 94 and bearing inhousing 5, namely, pinion 94 axially engages a frictional membercomprising a thrust washer 97 in housing 5, see FIG. 2. Thrust washer 97has a coefficient of friction on its engagement surface with pinion 94.The frictional force created by the engagement between washer 97 andpinion 94 resists rotation of the pinion during operation, but moreparticularly, it prevents rotation of the pinion when it is desirablethat the worm and hence outer race remain motionless and hence axialdisplacement of the race part is restrained, for example, for a steadystate engine speed and hence steady state transmission operatingcondition. In such a steady state condition motor 96 is deactivate. Thefrictional counter surface for thrust washer 97 is the aluminum housing5.

Thrust washer 97 can be made of steel. It may also comprise a coating orover-molded friction surface on a steel insert.

Grease or light oil can be used for a non-coated steel thrust washer. Inthis case the coefficient of friction of the steel only washer isapproximately 0.9-1.1. In the case where it is necessary to reduce thecoefficient of friction below that of steel the following thermoplasticmaterials can be used (by way of example and not of limitation): ArlenAE 4200 (Mitsui Petrochemical), Lubricomp 189 (LNP Engineered Plastics).The coefficient of friction for the thermoplastic materials isapproximately 0.06 to 1.0. Oil or grease is not used with thethermoplastic materials.

In the case where it is necessary to increase the coefficient offriction above that of steel the following thermoplastic materials canbe used (by way of example and not of limitation): Lubriloy RL (LNPEngineered Plastics), TEP 642 (Thomson Industries). The coefficient offriction using these materials is approximately 0.14 to 1.20. Oil orgrease is not used with these thermoplastic materials.

Any of the foregoing thermoplastic materials can be molded over thesteel washer insert or may be used without a steel insert.

The described mechanical and frictional configuration results in theworm drive being self-locking when the motor 96 is not in operation. Thetorque provided by the motor 96 need only be sufficient to overcome thefrictional force between washer 97 and pinion 94 and the radial force ofthe members 25 to thereby cause rotation of the outer race part 26 a.Once the outer race is moved to a desired position, and hencetransmission output ratio, motor 96 is deactivated. The frictionalcharacteristic of the worm drive then prevents further rotation (andaxial movement) of the outer race 26 a by operation of the self-lockingpinion.

FIG. 10 is a cross-sectional view of the transmission. Referring also toFIG. 2 and FIG. 9 the inner ball screw comprises cooperating helicalchannels 37 and 38 with balls 39 cooperatively disposed therein. Forexample and not by way of limitation, the ball screw comprises a pitchdiameter of 18 mm, a lead of 9.57 mm and a ball diameter of 2.65 mm. Thehelix angle is 9.61 degrees. The ball screw comprises three starts. Thenumber of balls per start is 37 for a total number of 111 balls. Theaxial length over balls is 21.5 mm.

As described elsewhere in this specification, outer race part 26 b movesin direction ±D by rotating within outer race part 26 a in direction Ron ball screw 43, 44, 48, see FIG. 5. The ball screw has a pitchdiameter of 107 mm, a lead of 16.01 mm and a ball diameter of 3.00 mm.The helix angle is 2.73 degrees and has 4 starts. The number of ballsper start is 15. The total number of ball screw balls is 60. The axiallength over balls is 8.4 mm.

Pinion 94 is engaged in housing 5. Motor 96 is mounted directly tohousing 5 by means known in the art, such as by studs, bolts or screws.Splash lubrication by the traction fluid is provided to both ball screwsby rotation of planet cage 14.

FIG. 11 is a cross-sectional view of the tandem embodiment. In thisexample arrangement, air conditioning compressor AC is directly coupledto transmission 1000. An input clutch of AC is directly connected tooutput shaft 102, see FIG. 12. Fasteners 200 known in the art, forexample, bolts, studs or pins, are used to attach AC to housing 5 oftransmission 1000. Housing members 202 receive fasteners 200. Fasteners201 connect AC to an engine block. Fasteners 201 comprise studs, boltsor screws or any other suitable fastener known in the art.

In this embodiment dust cover 103 as shown in FIG. 10 is removed fromthe transmission to allow direct connection of the AC input clutch toshaft 102.

Dust cover 1001 protects belt B3 from debris.

FIG. 12 is a partial perspective view of the tandem embodiment. Themajority of transmission 1000 is deleted from this view with theexception of cage portion 14 b and shaft 102. Shaft 102 of cage portion14 b is shown directly connected to the air conditioner compressor inputclutch ACC. The air conditioner compressor operates at the same speed asoutput shaft 102. However, the air conditioner compressor does notnecessarily operate at the same speed as the driven accessories. Thespeed of the AC compressor is a function of the diameter of thecrankshaft pulley A and transmission input pulley 100 and thetransmission ratio. Hence, the speed of the compressor directly coupledas shown is determined in part by the diameter of the input pulley 100.On the other hand, the other accessories shown in FIG. 1 are driven byoutput pulley 101, which diameter can also be selected to give a desiredaccessory speed that is different or the same as the air conditionercompressor speed based on the diameter of each of the accessory pulleys.Hence, the tandem accessory arrangement allows two independent accessoryspeeds; one speed being that of the output shaft 102 and the other beinga function of the pulley ratios between pulley 101 and the variousindividual accessory pulley diameters. This provides broad variabilityfor system optimization.

FIG. 13 is a block diagram of the control system. Control hardware andsoftware comprise stepper motor controller microprocessor 98 (A) and thesoftware resident in the microprocessor memory. The software resident inthe microprocessor memory comprises a proportional-differential (PD)control scheme (B). Also stored in the memory for use by the software isa desired accessory speed (C). Microprocessor 98 receives signals from acrankshaft speed sensor and an accessory speed sensor.

The proportional-differential control implements an effective and simplecontrol strategy. The software calculates an error between a desiredaccessory speed (C) and an actual accessory speed (obtained by afeedback loop). It takes the calculated error between the desiredaccessory speed and the actual speed and scales it with a proportionalconstant and a differential constant. If there is a difference betweenthe desired accessory speed and actual accessory speed, an error signalis generated and transmitted to the stepper motor driver 97 that causesthe stepper motor 96 to adjust the transmission ratio to cause theaccessory speed to more closely match the desired speed. When the actualaccessory speed becomes equal to the desired accessory speed no errorsignal will be present and the stepper motor is deactivated. Asdescribed elsewhere, the self-locking worm gear drive and outer raceprevents the transmission from changing ratio while the stepper motor isdeactivated. The stepper motor can be driven by a 12V or 42 V system(D).

Description of System Performance

Using vehicle simulation software, for example, GT-Drive™ from GammaTechnologies, Inc., it is possible to quantify the benefits of theinventive CSAD system. The following exemplary discussion relates tosimulating the performance of a Ford Focus™ with a 2.0 L engine and afive speed manual transmission.

A map of the transmission efficiency is as follows:

Efficiency is in %, speed is in RPM's and torque is in N/m.

The significantly improved acceleration performance of the vehicle usingthe inventive system is shown in FIG. 14. FIG. 14 depicts vehicleacceleration performance differences between two example accessoryspeeds. Curve (B) depicts the performance of a prior art engine using aprior art asynchronous belt drive system (ABDS). In the prior art systemthe accessory drive speed is directly proportional to the speed of theengine crankshaft since the accessories are directly coupled to thecrankshaft by a single belt. By comparison, when the transmission outputpulley 101 is operated at a constant speed of approximately 885 RPM(Curve (A)) using the inventive system, an approximate 4.0 secondimprovement in the 0-60 MPH acceleration time is realized. 885 RPM isthe engine idle speed where the alternator generates approximately 70%of its rated current. When the accessories are operated at a constantspeed of 2000 RPM (Curve (C)), the minimum speed where the alternatorgenerates approximately 100% of its rated current, the elapsed 0-60 timeimprovement is just slightly less than approximately 4.0 seconds. Ineither case (A or C) operating the accessories at a constant speed at orless than the speed of the engine crankshaft significantly improvesvehicle performance by providing additional torque to the drive axlethat would otherwise be used driving the accessories.

FIG. 15 is a graph which shows that although the engine speedcontinuously varies as the transmission shifts gears, the speed of theaccessories remains substantially constant using the inventive CSADsystem. Namely, the speed of shafts 22 and 102 is substantially constantover the operating speed range of the crankshaft for essentially twoengine operating conditions, namely, comprising speeds in excess ofidle, and, the engine speed at idle. The power steering pump (PS), airconditioner (AC) compressor, alternator (ALT) and water pump (WP) alloperate at substantially constant speeds for each of the two operatingconditions, although the alternator speed is relatively higher than thespeed of the other accessories. The speeds illustrated in FIG. 15 areonly provided as an example of relative operational characteristics ofdrive components and not as limiting accessory speeds for a system.

Contrasting the inventive system with the prior art, FIG. 16 shows thespeed behavior of a prior art system with a fixed ratio accessory driveconnection to the crankshaft. The speed of the accessories (B), (C), and(D) is directly proportional to the speed of the crankshaft (A) sincethe accessory drive is directly coupled to the crankshaft by a belt.This prior art form of operation is inefficient since each accessorymust be able to operate satisfactorily over the broad speed rangepresented by the crankshaft.

FIG. 17 depicts an exemplary gear ratio variation for the transmissionto maintain a constant speed behavior of the accessory drive.

Exemplary fuel efficiency improvements are shown for other accessoryspeeds:

The “%” values indicate the percentage of time the AC (air conditioner)and Alt (alternator) are in operation. For example, one can see that forthe city cycle at 1400 RPM with the AC 100% and Alt 100%, the % increasein MPG is approximately 11%. Likewise for highway cycle, the % increaseis approximately 11%.

The described analysis was also performed on a 5.3 L SUV engine with thefollowing results:

Table 1, below, illustrates the expected improvement in fuel economy forthe European drive cycle shown in FIG. 18 for the 2.0 liter engine.Table 1 takes into account the torque transmitting efficiency of thetransmission which is estimated at approximately 90%. However, theefficiency of the transmission need only be above approximately 85% inorder to realize the estimated fuel savings if the accessory speed iscontrolled to approximately 2000 RPM. The alternator is continuouslyoperated at approximately 5000 RPM+ to realize maximum efficiency. Thesystem can tolerate a lower transmission efficiency (<85%) if theaccessory speed is set to approximately 850 RPM. The improvement of theinventive system over the prior art system is illustrated in Table 2.TABLE 1 Fuel Economy for Different CSAD Efficiencies over European Cycle100% 95% 90% 85% Efficiency Efficiency Efficiency Efficiency CSAD at 850RPM 31.2 mpg 30.9 mpg 30.5 mpg 30.1 mpg CSAD at 2000 RPM 28.6 mpg 28.5mpg 28.1 mpg 27.6 mpg Present System 27.4 mpg 27.4 mpg 27.4 mpg 27.4 mpg

TABLE 2 Improvements of CSAD System over Present Fixed Ratio System 100%95% 90% 85% Efficiency Efficiency Efficiency Efficiency CSAD at 850 RPM+13.9% +12.8% +11.3% +9.6% CSAD at 2000 RPM  +4.4%  +4.0%  +2.6% +0.8%Present System — — — —

Further, under constant speed driving, such as that experienced on ahighway, significant fuel savings are also realized as well. This isillustrated in Table 3 where the efficiency of the inventive CSADtransmission is assumed to be approximately 85%. Of course, asefficiency varies so does the fuel savings at constant speed. TABLE 3Fuel Savings at Constant Vehicle Speed 80 km/hr 100 km/hr 120 km/hr CSADat 850 RPM +17.4% +11.2% +12.8% CSAD at 2000 RPM  +6.4%  +2.9%  +6.4%Present System — — —

Since the accessories are driven at a substantially constant speed,accessories such as the air conditioner compressor and alternator can bedesigned to be the most efficient at the chosen constant speed ratherthat being designed to have good performance over the entire enginecrankshaft speed range. Further, parasitic losses of a hydraulic powersteering unit can be minimized with the inventive system over the priorart by operating it at a lower speed.

Although forms of the invention have been described herein, it will beobvious to those skilled in the art that variations may be made in theconstruction and relation of parts without departing from the spirit andscope of the invention described herein.

1. A method of operating a belt drive accessory system comprising thesteps of: transmitting a torque with a first endless member from adriver member to a planetary ball transmission input; coaxially aligningthe planetary ball transmission input with a planetary ball transmissionoutput; transmitting a torque by a second endless member from theplanetary ball transmission output to a driven accessory; selecting aspeed ratio of the planetary ball transmission according to a drivermember rotational speed, thereby operating the driven accessory at asubstantially constant speed at a point of substantially maximumefficiency over a drive member rotational speed range; and frictionallylocking the speed ratio of the planetary ball transmission when a drivemember speed is constant.
 2. The method as in claim 1 comprising thestep of connecting a driven member directly to a planetary balltransmission second output.
 3. The method as in claim 1 comprising thestep of tensioning the second endless member with a tensioner.
 4. Themethod as in claim 3 comprising the step of damping an oscillation ofthe second endless member.
 5. The method as in claim 1 comprising thestep of tensioning the first endless drive member with a tensioningmember.
 6. The method as in claim 1 comprising the step of damping anoscillation of the first endless member.
 7. The method as in claim 1comprising the step of a one-way clutching action for a driven accessoryoverrunning condition.
 8. The method as in claim 1 comprising the stepsof: calculating an error between a desired accessory speed and an actualaccessory speed; and adjusting a transmission ratio until no substantialerror signal is generated.
 9. A transmission comprising: input andoutput drive members; radially inner and outer races; planetary membersin rolling contact with said radially inner and outer races; said innerrace and said outer race each comprising two axially spaced partsconnected for rotation together and relatively axially moveable; meansfor selectively varying the axial separation of said two axially spacedparts of one of said races and thus the radial position of the planetarymembers in rolling contact therewith comprising an adjustment member anda helical interengagement member interconnecting said adjustment membersuch that relative turning motion of said adjustment member results inrelative axial displacement of the adjustment member; a self lockingdrive comprising a drive motor and a worm gear engaged with theadjustment member and a thrust washer having a frictional coefficientengaged with the worm gear, the self locking drive preventing relativeturning motion of the adjustment member when the drive motor is notenergized; and torque sensitive means sensitive to the torque appliedbetween two drive-transmitting members of the transmission comprising abiasing member and a second helical interengagement member acting toreact the forces exerted by the transmission of drive forces between theradially inner race and the planetary members, said torque sensitivemeans acting both to determine the compensating variation in theseparation of the parts of the other race and thus the transmissionratio of the device and to vary the forces exchanged between theplanetary members and the races normal to the interface between them.10. The transmission as in claim 9 wherein the planetary members aresubstantially spherical and the transmission of forces between theplanetary members in planetary motion and one of said input drive memberand output drive member is effected via follower members, each followermember comprising a substantially arcuate concave form.
 11. Thetransmission as in claim 9 wherein the output means comprises dualcoaxial output members.